Reduction of Probe-Spacing Effect in Pulsed Eddy Current Testing

In using pulsed eddy currents to determine the thickness of cladding, it was found that the output wave as observed on the screen of a cathode-ray oscilloscope had several unusual points. These points were stationary as the probe-to-metal spacing varied, but moved vertically as the cladding thickness changed. Tests on a clad plate seemed to indicate that the points could be used to determine cladding thickness with little interference from changes in the probe-to-metal spacing. One such method involves the use of small photocells placed in front of the oscilloscope screen with the output of the photocells connected to a recorder. The initial tests with such a system are presented in this paper.